Microstructure-informed Hydrogen embrittlement life prediction of Nickel-based alloys (Helife)

Nickel-based alloys (NBAs) are used in many industries, including oil and gas, due to their high strength, corrosion resistance, and expected resistance to hydrogen embrittlement (HE). However, HE has been known to cause failures in NBAs, and it is now understood that all NBAs are susceptible to HE, to varying degrees. The oil and gas industry is concerned about the risk of HE in NBAs, and they are working together to develop a practical guideline for assessing HE in existing NBA components and potential new promising alloys. The guideline will require a solid understanding of the HE mechanisms in NBAs, reliable HE resistance testing methods, and a predictive framework for integrity assessment and life prediction. The project is therefore focused on three main areas: 1) Understanding the effect of microstructure on hydrogen diffusion and embrittlement mechanisms. We will study how the microstructures of both existing and new materials affect the way hydrogen diffuses into the metals and how it interacts with the metals'. 2) Developing a mechanistic hydrogen failure model. We will develop a model that can predict how hydrogen embrittlement will affect the strength and toughness of NBAs. 3) Providing the basis for establishing a reliable testing method. Together with industrial partners, the project will develop testing methods that can be used to validate the hydrogen failure model. The project is expected to provide a better understanding of hydrogen embrittlement in NBAs and to develop methods for assessing the risk of HE in existing and new alloys. This results will help ensure the safety and reliability of NBAs in the oil and gas industry. Updates as of October 1, 2024 Significant progress has been made in both the experimental and simulation aspects of the project over the past period. Experimental Progress: The microstructures of four nickel alloys, all involved in the DNV JIP project, have been examined at NTNU using advanced experimental techniques. Notably, the development of the DL-EPR technique, which was specifically requested by industrial partners, was completed ahead of schedule. Although non-standard, DL-EPR shows great promise as a method for screening and identifying detrimental microstructures. Simulation Progress: DNV is currently developing an industrial guideline based on the local strain concept for assessing hydrogen embrittlement (HE) risk in engineering components. It was initially hypothesized that the critical strain in a hydrogen environment would increase with the stress concentration factor. However, our simulation results, using the advanced H-CGM+ predictive model, suggest that critical strains may not always increase monotonically with stress concentration factor. We also noted that failure location can differ between air and hydrogen-charged conditions depending on specimen thickness, and the critical local strain appears to be influenced by the hydrogen concentration within the material.

Nickel-based alloys (NBA) are widely used in the oil and gas industry because of their superior corrosion resistance, excellent mechanical strength and expected immunity to hydrogen embrittlement (HE) or hydrogen induced stress cracking. With multiple failures reported over the last years, it is now commonly accepted that all nickel alloys are susceptible to HE, however, some are less susceptible than others. Because of the slow hydrogen diffusion in nickel alloys, a failure caused by HE which is one of the costliest failures in the industry, may occur after decades in service. Alarmed by this “time bomb” scenario, the oil and gas industry in Norway is attempting to establish a practical guideline for assessing HE in both existing NBA components and in potential new hydrogen resistant alloys. Known as a conspicuous material challenge, HE is the outcome of the complex interactions of triple families of parameters - susceptible microstructures, hydrogen environment and mechanical loading. Establishing such an industrial guideline requires a solid understanding of the HE mechanisms of relevant materials, reliable HE resistance testing methods and a predictive framework for integrity assessment and life prediction. The primary objective of this project is to provide the scientific basis needed for establishing the practical guideline with respect to HE in existing NBA and the potential new alloys for the subsea applications. The secondary objectives are to probe the HE mechanisms of the in-service precipitation hardened nickel alloys (PHNA) with special emphasis on the embrittling effect of grain boundary precipitates; to study the hydrogen diffusion and hydrogen-coupled deformation mechanisms in selected strain hardened austenitic alloys; to provide basis for developing model-guided testing methods for retrieving transferrable model parameters; to establish and verify a microstructure-informed HE predictive framework for integrity assessment.